Conventional methods for making the surface of materials soil cleaning comprises treating the surface to confer the ability to remove stains or soils deposited on the surface. In other methods, excellent oxidative degradation activity of a photocatalyst fixed onto the surface is utilized to degrade organic matter or stains or soils deposited on the surface and also any gaseous pollution which comes into contact with the surface.
In particular, heterogeneous photocatalysis has efficiently been used for oxidizing and thereby removing unwanted compounds from fluids, including water, and air. Thus, UV-illuminated catalyst, such as titanium dioxide, absorbs UV light, which produces electrons and holes that migrate to the surface of the catalyst. At the surface, the electrons reduce adsorbed oxygen, while the holes oxidize organic compounds or adsorbed water molecules.
However, satisfactory depolluting properties may not be provided with only such a single photocatalytic coating composition for a long lifetime i. e. over 5 years.
Accordingly, it is an object of the present invention to provide a coating composition which, independently of environment, such as indoor or outdoor environment, can semi-permanently and in a single coating exhibits excellent surface depolluting properties, particularly excellent soil cleaning activity against greasy stains, including mildew, mold, algae or soils.
For various reasons, including cost and desired properties, there is always a need to develop new and better depolluting coating compositions.